A quick test in a new repository shows that delta storages is used for the second revision of a file.
% svn add iota % svn ci -mm % echo>>iota % svn ci -mm % svn info iota Last Changed Revision: 2 % grep DELTA ../r1/db/revs/0/2 Binary file 2 matches Mark Phippard wrote on Mon, Aug 08, 2011 at 13:31:58 -0400: > On Mon, Aug 8, 2011 at 12:49 PM, Jon Stafford > <jon.staff...@complyserve.com>wrote: > > > I'm trying to understand why subversion isn't just storing diffs of some > > binary files. It looks like it’s taking up more space than it needs to.** > > ** > > > > ** ** > > > > At length the issue is described here: > > http://stackoverflow.com/q/6917505/277208**** > > > > ** ** > > > > The more summarized version is...**** > > > > ** ** > > > > I understand that subversion stores files differentially (compressed), even > > for binary files. And subversion uses Xdelta to help with this.**** > > > > ** ** > > > > I can do a standalone xdelta on my 50MB zip files:**** > > > > xdelta3.0z.x86-64.exe -e -s v1_path\data.zip v2_path\data.zip > > v1v2_delta.file**** > > > > ** ** > > > > and get a nicely small v1v2_delta.file which is about 3MB.**** > > > > ** ** > > > > But when I check successive versions of the data.zip into a subversion > > repository (FSFS, version 1.6.11) I get two ~50MB files in db\revs\0**** > > > > ** ** > > > > I appreciate minimizing disk usage isn't the only thing, e.g. performance > > may be more important. Being able to configure this would be useful in my > > situation.**** > > > > ** ** > > > > I've spent a long time trying to figure out what is going on and not got > > very far. I guess this behaviour is probably deliberate - it would be > > really interesting to have an idea of different factors deciding subversion > > behaving in this way. > > > > There are no knobs you can turn, and SVN internally does not have any > heuristics it goes through where it decides not to produce deltas. It > always produces deltas, even when it is a waste of CPU to do so. > > However, the fsfs backend also uses a technique called "skip-deltas" which > you can read about here: > > http://svn.apache.org/repos/asf/subversion/trunk/notes/skip-deltas > > Have you only done two commits of this file? Reading the above note, it > looks like the first two revisions of the file are stored as full revisions. > > -- > Thanks > > Mark Phippard > http://markphip.blogspot.com/
